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A study of the two most popular weight-loss surgeries found obese diabetics who had gastric bypass surgery lost 64 percent of their excess weight after a year, compared with 36 percent in those treated with Allergan Inc's Lap-Band device, researchers said on Monday.

Rates of women who are opting for preventive mastectomies, such as Angeline Jolie, have increased by an estimated 50 percent in recent years, experts say. But many doctors are puzzled because the operation doesn't carry a 100 percent guarantee, it's major surgery -- and women have other options, from a once-a-day pill to careful monitoring.

"It's a dramatic difference," said Dr. Guilherme Campos of the University of Wisconsin School of Medicine in Madison, and formerly of the University of California, San Francisco, whose study appears in the Archives of Surgery.

Weight loss surgery is becoming increasingly popular as obese people struggle to lose weight and avoid the health complications that accompany the extra pounds -- including diabetes, heart disease, joint pain and some cancers.

Rates of women who are opting for preventive mastectomies, such as Angeline Jolie, have increased by an estimated 50 percent in recent years, experts say. But many doctors are puzzled because the operation doesn't carry a 100 percent guarantee, it's major surgery -- and women have other options, from a once-a-day pill to careful monitoring.

In this study, researchers compared Allergan's Lap-Band device with a form of gastric bypass surgery known as Roux-en-Y. The surgery was done laparoscopically -- through small incisions in the belly.

The study involved 100 morbidly obese people who underwent Lap-Band surgery. These patients were matched by sex, race, age and weight with 100 patients who underwent gastric bypass.

All of the bypass surgeries were performed by expert surgeons in high-volume weight loss centers.

"In the gastric bypass patients, about 86 percent of patients successfully lost more than 40 percent of excess weight. Only about 31 percent of the Lap-Band patients lost that amount of weight," Campos said in a telephone interview.

"That is significant," he said.

Overall, 12 percent of patients in the Lap-Band group and 15 percent of patients in the gastric bypass group experienced complications. Patients who got gastric banding were more likely to have complications right after their surgeries, while Lap-Band patients were more likely to need a second operation. There were no deaths in either group.

The study shows that gastric bypass provides better weight loss, better resolution of diabetes and an improvement in quality of life compared to the Lap-Band, Campos said.

He said obese patients need to be informed of the results of the two procedures, and if they choose gastric bypass they need to make sure their surgeon is highly experienced.